Electromagnetic phono cartridge

ABSTRACT

A stylus for an electromagnetic phono cartridge which comprises a tubular ferromagnetic armature mounted on the flat side of a permanent magnet. The armature extends coaxially from the permanent magnet to a cantilever in the opposite direction. The permanent magnet is housed inside a nonmagnetizable shell which is located between a pair of pole pieces having coils in the phono cartridge. A flexible sleeve covers the entire circumference of the outer narrow side of the permanent magnet to hold the stylus in the nonmagnetizable shell.

States Patent 1 1 1111 3,924,076

Dubois Dec. 2, 1975 [54] ELECTROMAGNETIC Pl-lONO CARTRIDGE 3.463.889 8/1969 Ahrens 179/1004] K 3,538,266 11/1970 Cho l79/lO().4l K [75] lnvemor- 5" Dubms, Colombler, 3.576.955 5 1971 Obata 179/10041 M swltzerland 3.761.647 9 1973 Ncmoto et 111...... 179/100.41 K

[73] Assignee: Huber & C0., Hauterive,

S i l d Primary ExaminerBernard Konick 7 Assistant Examiner-Stewart Levy Flled' 1973 Attorney. Agent, or FirmBrowdy and Neimark [21] Appl. No: 425,852

[57] ABSTRACT [30] Foreign Application Priority Data A stylus for an electromagnetic phono cartridge which May 29 1973 Switzerland 7753/73 comprises a tubular ferromagnetic armature mounted on the flat side of a permanent magnet. The armature 152 0.5. c1. 179/100.41M* 179/100 41 14 extends axially from the Permanent mgne 51 1111.0. H04R i1/12 cantilever the opposite direcmn- The Permanent [58] Field 61 Search 179/10041 .1 100.41 K magret is used inside "Onmagnetizable 179/100 274/37 which is located between a pair of pole pieces having coils in the phono cartridge. A flexible sleeve covers [56] References Cited the entire circumference of the outer narrow side of the permanent magnet to hold the stylus in the non- UNITED STATES PATENTS magnetizable Shell. 3,349,194 10/1967 Shaper 179/100.41 1 3,356.795 12/1967 Shaper 179/10041 K 10 ClaImS- 4 Drawmg Flgures US. Patent Dec. 2, 1975 3,924,076

ELECTROMAGNETIC PHONO CARTRIDGE FIELD OF THE INVENTION The present invention relates to a stylus for an electromagnetic phone cartridge, with an armature containing a lamellar permanent magnet magnetized in the axial direction, the magnet being connected to a cantilever provided with a stylus tip or needle.

BACKGROUND OF THE INVENTION Prior styli of the above type have as a armature a permanent magnet consisting of a flat plate, magnetized with the same polarity on both outer sides and with opposite polarity at the center. Furthermore, the cartridge is provided with at least one essentially inverted ring-shaped yoke, a pair of pole pieces mounted in the vicinity of the armature and a coil wound around the yoke. In addition, the cantilever supporting the stylus tip has an axial extension as a mount, the extension being linked to the cantilever or to the permanentmagnetic plate by means of an elastic connection, in such fashion that the plate moves essentially with its central section as the working point.

The disadvantage of these known styli is the fact that the yoke must extend perpendicular to the axis of the permanent magnet, resulting in cartridge with a large cross section. A further disadvantage consists in the fact that the permanent magnet must be composed of two individual magnets, since the type of magnetization described above is either impossible or very difficult to achieve with a single magnet.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the defects in the prior art, such as indicated above.

Another object is to provide for improved electromagnetic phone cartridges.

Another purpose of the present invention is to further reduce the inert mass of the armature which constitutes the moving part of a cartridge, and, simultaneously, to produce a mount for the stylus which is light, has low friction, and which results in a cartridge with a small cross section.

The stylus described below uses permanent magnetic materials with a high coercive force and high magnetic energy, for example Samarium-cobalt (Sm-Co), which has a coercive force H of 4 to kOe and a magnetic energy B.H. of approximately 18 kOe/g.

To achieve the desired purpose, the stylus according to the instant invention is characterized by a tubular ferromagnetic armature which is mounted on one face of the permanent magnet. The armature extends out coaxially from the permanent magnet to the abovementioned cantilever in the opposite direction. The permanent magnet is provided on its outer narrow side over its entire circumference with a flexible sleeve to hold the stylus in a shell which is non-magnetizable and is located between the pole pieces of the cartridge, the pole pieces being provided with coils.

BRIEF DESCRIPTION OF THE DRAWING Sample non-limitative embodiments of the subject of the invention will be described below with reference to the drawing.

FIG. 1 is a lengthwise cross-sectional view through a stylus made according to the instant invention, without the stylus tip holding element.

FIG. 2 is a side elevational view of the stylus shown in FIG. 1.

FIG. 3 is a front elevational view of the stylus in FIG. 2 mounted in a housing located between a plurality of pole pieces.

FIG. 4 is a lengthwise cross sectional view of the arrangement shown in FIG. 3, including the magnetic lines of force.

DETAILED DESCRIPTION Referring now to FIGS. 1 and 2, the illustrated stylus has a disc-shaped permanent magnet l, which may consist, for example, of the initially mentioned samariumcobalt or a similar permanent magnetic material with high coercive force and high magnetic energy. A tubular armature 2 is attached to one end face of the permanent magnet l, the armature 2 being made, for example, of Armco iron. Armature 2 has a first segment 3, whose axial length is at least approximately equal to the thickness of permanent magnet 1 and whose outer diameter is equal to the outer diameter of permanent magnet l. The end face of the first segment 3 of the armature 2 is fastened to the end face of permanent magnet 1 by means of a suitable adhesive layer 4, e.g., an

epoxy resin.

A second segment 5 of the armature 2 is connected to the first segment 3 of the tubular armature, the second segment having an outside diameter and wall thickness less than those of the first segment 3, but whose axial length is greater than that of the first segment. The ratio of the diameter of the permanent magnet l to its thickness is in the range from 2 to 10, while the ratio of the axial length of the tubular armature section 2 to the thickness of the permanent magnet is in the range from 4 to 10. For example, the outside diameter of the permanent magnet 1 may be 25 mm and its thickness 0.5 mm, while the armature section 2 then may have a length of 2.5 mm. The transition 6 from the first segment 3 with the larger outside diameter to the second segment 5 with the smaller outside diameter is advantageously continuous, as can be seen from FIG. 1 and 2.

A flexible sleeve 7, which has a convex cross section in the stretched state, is applied to the common surface of the narrow sides of the permanent magnet l and the first segment 3 of the tubular armature section 2.

The permanent magnet 1 has a central bore whose diameter is equal to that of the bore of the first segment 3 of tubular armature section 2. This common central opening contains a tube section 8, made of a light metal and fastened in place, such as by epoxy resin. Tube section 8 serves, on the one hand, to accept a tubular cantilever 9 made of a light metal alloy (e.g. a magnesium alloy which is pushed onto tubular section 8 and fastened to the latter (see FIG. 2). The free end of cantilever 9 is fitted with a stylus tip 10, preferably a diamond needle. The tube section 8 serves, on the other hand, as a mount for a wire spring 11 whose function will be described below. The spring 11 is fastened centrally in tube section 8 by means of a drop of adhesive 12.

The stylus described in FIG. 1 and 2 is pushed into a shell with a square cross section (shown in FIG. 3) when the phono cartridge is assembled, the shell being made of a nonmagnetizable material, e.g., brass. The four points of support 14 of elastic sleeve 7 on the internal surface of shell 13 ensure a free movement, hindered only by extremely low frictional forces, of cantilever 9 supporting stylus tip 10 in a conical region whose apex is located at the center of the common plane of permanent magnet 1 and the first segment 3 of the tubular armature section 2. Advantageously, this stylus is made so that this point is simultaneously the center of gravity of the stylus.

FIG. 3 also shows the pole discs and 16, each associated with the core of the magnet, arranged in pairs on the outside of the shell 13, said pole discs extending lengthwise along the shell 13 and connected together in known fashion by yokes, said yokes each carrying one coil in which voltages are induced when cantilever 9 is deflected. When a stereo record is played, stylus tip 10 moves in mutually perpendicular directions 17 and 18 in accordance with the two recording channels, so that, as will be described below, the magnetic flux in the pole pieces 15 and 16 changes. When playing a mono record, the stylus tip moves in a horizontal direction 19, so that the same change in flux is caused in two mutually perpendicular pole pieces 15 and 16.

The mode of operation of the stylus in a phone cartridge is shown in FIG. 4, which shows a lengthwise cross-sectional view of the arrangement shown in FIG. 3 at a 45 angle. In FIG. 4, a portion of the stylus according to FIG. 1 and 2 with permanent magnet 1, the tubular ferromagnetic armature section 2 which consists of segments 3 and 5, flexible sleeve 7 and cantilever 9 are visible. The stylus is held by means of the flexible sleeve 7 in the nonmagnetizable square shell 13 which is mounted in turn between a pair of pole pieces 15. It can also be seen from FIG. 4 that the free end of the wire spring 11 is connected to the shell. In the sample embodiment shown, the wire spring 11 is clamped firmly in place by means of plate 20 which is made of an insulating material that is pressed into shell 13. Spring 11 serves to compensate for the weight of the tone arm when the stylus tip rests on the record. The free end of the spring is fastened to the opposite side of the point of the stylus tip 10 with respect to the lengthwise axis of the stylus at shell 13.

FIG. 4 also shows that both pole pieces 15 constitute portions of a magnetic core which has a yoke 21 on which a coil 22 surrounding the yoke is fastened in known fashion. A magnetic core arrangement mounted in the phono cartridge in the same fashion contains pole pieces 16 in FIG. 3.

In FIG. 4, the pattern of the magnetic field or magnetic flux is represented schematically by individual lines. Permanent magnet l is magnetized in the axial direction so that armature section 2 is likewise magnetized in the axial direction. The corresponding magnetic poles are represented by N and S.

Due to the short axial length of permanent magnet 1 and the first segment 3 of armature section 2 which connects to it, and also because of the high magnetic energy of permanent I, the scattered lines of force 23 run essentially parallel to the axis of permanent magnet l and of the first segment 3 of armature section 2 and very closely along their surfaces in the regions of maximum and undesirable attraction. This means that undesirable attraction by yokes l5 and 16 is almost completely avoided.

The useful magnetic field represented by lines of force 24 runs from the indicated North pole of permanent magnet l with equal amplitude to each pole piece 15 and from the letter to the South pole of the free end of the tubular armature section 2. The magnetic field is therefore completely symmetrical with respect to pole pieces 15 when the stylus is at rest.

When the cantilever 9, supporting the stylus tip, is deflected upward as in FIG. 4 (i.e., when the free end of armature section 2 approaches the lower pole piece 15) the magnetic field runs primarily along the schematic line of force 25 and, therefore, causes a magnetic flux in yoke 21 which induces a voltage in coil 22. A magnetic flux in the opposite direction is induced in yoke 21 when the stylus tip and, therefore cantilever 9 move in the opposite direction.

The present stylus has a mass which is much less than that of known styli for electromagnetic phono cartridges, especially as far as the mass of the armature is concerned.

The direct connection of permanent magnet l with armature section 2 also results in increased efficiency so that in the case of the stylus which is mentioned for the sake of an example, with equal magnetic energy, a reduction of mass of the armature by a factor of 5 is achieved. Due to the small dimensions of the permanent magnet, the latter can be used advantageously for mounting the armature directly in a nonmagnetizable shell. This means that the part of the armature which has the greatest mass is located in the region with the least movement when a record is played. At the same time, this mounting of the stylus at four points results in a considerable reduction of harmful influences of the flexible sleeve due to the deformations of the flexible material that result from known types of mounting (e.g., in the corner areas of the square shell). The frictional areas of the mount are very small in the case of the instant stylus. In addition, due to the smallermass of the stylus which must be mounted, lesser harmful frictional forces result.

In the sample embodiment described above, the permanent magnet 1 and the contiguous segment 3 of the tubular armature have circular or cylindrical shapes, while the nonmagnetizable shell 13 has a square internal cross section. It is naturally possible to reverse these shapes although it is less simple to do so.

It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.

What is claimed is:

1. An electromagnetic phono cartridge comprising:

a lamellar axially magnetized permanent magnet said permanent magnet having a flat side, an outer circumferential narrow side and an end face; non-magnetic cantilever provided with a stylus tip connected to said permanent magnet; ferromagnetic armature tube directly mounted on the end face of said permanent magnet, said armature extending coaxially from the permanent magnet to the cantilever in the opposite direction, and wherein said armature tube includes a first segment connected to the end face of said permanent magnet, said first segment having transverse dimensions approximately equal to those of said permanent magnet; flexible sleeve means for covering the entire circumference of the outer narrow side of said permanent magnet; nonmagnetizable shell means having an inner surface and housing said permanent magnet, said armature and a portion of said cantilever adjacent said permanent magnet; said flexible sleeve means being in contact with said inner surface of said shell means at a plurality of points for supporting said permanent magnet, armature and cantilever; and

a pair of pole pieces substantially enclosing said shell means, said pole pieces including coils in the phono cartridge.

2. The stylus of claim 1, wherein said armature tube has a second segment, said second segment having external cross sectional dimensions and a wall thickness less than those of said first segment and having an axial length greater than that of said first segment, wherein the axial length of the first segment is approximately equal to the thickness of the permanent magnet.

3. The stylus of claim 1, wherein said flexible sleeve means is located on the narrow side of permanent magnet and said first segment of said tubular armature.

4. The stylus of claim 2, wherein the external cross section of said first and second segments tapers from said first segment of said tubular armature to said second segment. 1

5. The stylus of claim 1, wherein said shell means is rectangular and wherein said permanent magnet and said first segment of said armature tube have a circular cross section for mounting in said rectangular shell means.

6. The stylus of claim 1, wherein said shell means is cylindrical and wherein said permanent magnet and said first segment off said armature tube have a square cross section for mounting in said cylindrical shell.

7. The stylus of claim 1, wherein said cantilever includes a tubular member of light metal and wherein said permanent magnet and said first segment of said armature tube each have a central bore, said tubular member being fastened within said bores.

8. The stylus of claim 7, comprising a spring having an outer end fastened to said tubular member, said outer end of said spring being connectable with said nonmagnetizable shell means.

9. The stylus of claim 1, wherein the ratio of the maximum diagonal dimension of said permanent magnet to the thickness of said permanent magnet is the range from 2 to 10 and the ratio of the length of said armature tube to the thickness of said permanent magnet is in the range from 4 to 10.

10. The stylus according to claim 1, wherein said permanent magnet is made of Samarium-cobalt. 

1. An electromagnetic phono cartridge comprising: a lamellar axially magnetized permanent magnet said permanent magnet having a flat side, an outer circumferential narrow side and an end face; a non-magnetic cantilever provided with a stylus tip connected to said permanent magnet; a ferromagnetic armature tube directly mounted on the end face of said permanent magnet, said armature extending coaxially from the permanent magnet to the cantilever in the opposite direction, and wherein said armature tube includes a first segment connected to the end face of said permanent magnet, said first segment having transverse dimensions approximately equal to those of said permanent magnet; flexible sleeve means for covering the entire circumference of the outer narrow side of said permanent magnet; nonmagnetizable shell means having an inner surface and housing said permanent magnet, said armature and a portion of said cantilever adjacent said permanent magnet; said flexible sleeve means being in contact with said inner surface of said shell means at a plurality of points for supporting said permanent magnet, armature and cantilever; and a pair of pole pieces substantially enclosing said shell means, said pole pieces including coils in the phono cartridge.
 2. The stylus of claim 1, wherein said armature tube has a second segment, said second segment having external cross sectional dimensions and a wall thickness less than those of said first segment and having an axial length greater than that of said first segment, wherein the axial length of the first segment is approximately equal to the thickness of the permanent magnet.
 3. The stylus of claim 1, wherein said flexible sleeve means is located on the narrow side of permanent magnet and said first segment of said tubular armature.
 4. The stylus of claim 2, wherein the external cross section of said first and second segments tapers from said first segment of said tubular armature to said second segment.
 5. The stylus of claim 1, wherein said shell means is rectangular and wherein said permanent magnet and said first segment of said armature tube have a circular cross section for mounting in said rectangular shell means.
 6. The stylus of claim 1, wherein said shell means is cylindrical and wherein said permanent magnet and said first segment off said armature tube have a square cross sectioN for mounting in said cylindrical shell.
 7. The stylus of claim 1, wherein said cantilever includes a tubular member of light metal and wherein said permanent magnet and said first segment of said armature tube each have a central bore, said tubular member being fastened within said bores.
 8. The stylus of claim 7, comprising a spring having an outer end fastened to said tubular member, said outer end of said spring being connectable with said nonmagnetizable shell means.
 9. The stylus of claim 1, wherein the ratio of the maximum diagonal dimension of said permanent magnet to the thickness of said permanent magnet is the range from 2 to 10 and the ratio of the length of said armature tube to the thickness of said permanent magnet is in the range from 4 to
 10. 10. The stylus according to claim 1, wherein said permanent magnet is made of samarium-cobalt. 